Although this invention is primarily directed to an improved stationary incinerator structure adapted to utilize solid fuel such as household and industrial waste, it will be understood that any of various types of combustible, particulate materials may serve as the supply fuel feed for the instant apparatus. The term "mass fuel" referred to herein, is intended to mean any matter being combusted while resting on a surface or traveling on or along a surface. This is to be distinguished from the prior art methods in which the matter is purposefully suspended in air a substantial distance above a surface. It is also distinguishable from prior art methods which require the matter to be fragmented before combustion.
The difficulty of burning certain mass fuels such as refuse is well-known. Refuse often includes a high percentage of slow-burning or wet materials which impede combustion and exhibit an erratic burn rate. Furthermore, such compositions vary continuously with the weather, season, area where picked up, conditions under which stored and other uncontrollable and unpredictable variables.
One known method of burning refuse is to divide the incinerator grate into two or three separate treatment zones and, through plenum chambers, provide combustion air under differing parameters to each one, thereby varying the characteristics of the air to suit the combustion needs. Thus, the air in the first zone containing fresh unburned refuse may be heated to dry out the trapped moisture, with combustion possibly not commencing until the refuse has entered the next zone, which is supplied with a different air mix.
Control of combustion in the various zones is generally limited to varying the characteristics of the air flowing to each zone. However, as the thickness of the refuse layer and its characteristics are generally not uniform across any one zone, burning time is longer, dictated by the slowest burning area on the grate.
It is, therefore, desirable to divide the grate surface into more zones and to provide means for independently controlling the combustion in each zone. Furthermore, the control should be as automatic as possible, so that each zone can be monitored and adjusted continuously, in an effort to maximize the efficiency of the burning to obtain the greatest throughput, be it solely an objective to dispose of an input feed material, or alternately to produce a source of energy, such as heated air, water or steam from the burning operation. Optimal burn efficiency is believed to be achieved only by the simultaneous mix and burn method previously known to those skilled in the art, but may be performed in a variety of manners.
It is also desirable to provide a means for mixing, or agitating the fuel during the combustion process. This mixing will enhance combustion by exposing all material to be combusted on the stationary surface where combustion is occurring. The result is such that the overall combustion efficiency is improved. One method used by those skilled in the art for performing this task prior to the present invention has been to design a stepped grate, whereby a part or all of the steps move in a fashion which in turn aids in the overall mixing and travel of the fuel in a predominant direction. This is in sharp contrast to the present invention which utilizes a stationary grate surface.
Another previously known means to accomplish the mixing is with the combustion air being fed through the grate assembly. However, the use of combustion air for this dual purpose presents problems that until the present invention were unseen by those skilled in the art. The problem was that while controlling combustion as well as enhancing the combustion through the mixing 10 of the fuel, neither of the tasks were optimized. Hence, while maintaining the required combustion air to support the overall combustion process, the specific requirements needed for the mixing may be neglected. Similarly, while maintaining the requirements needed to perform the mixing of the fuel, the necessary requirements for the proper oxygen-to-fuel ratio may be neglected either with too much or too little air. Combined with the need to adjust to varying fuel conditions in many cases, the ability to perform both tasks is virtually impossible. Therefore, a means for accomplishing both tasks in a fashion in which neither of these requirements are neglected would provide a drastic improvement in the overall combustion process.
For purposes of discussion, the term "combustion gas" referred to herein shall mean any gas such as atmospheric air or combustion air which contains similar or sufficient quantities of oxygen to support a combustion process.